Trustful relay is utilized to build up the long haul trunk QKD [1]} but the many relay stations must be well isolated and trustful. Meanwhile, quantum repeater [2]}, [3]} has been invented to replace optical amplifier. But the current technology can only reach 50 km [4]}, [5]}. Recently, it has been shown that there exists an upper bound for both repeater-less QKD or OFC [6]}. Therefore, the current main challenge towards large scale fiber quantum communication network is to beat the repeater-less bound and demonstrate QKD over real long haul trunk line.
